Water Vapour Adsorption Measurements on Metal Surfaces

A method of measuring the water vapour desorbed/adsorbed on electro-polished stainless steel (EP-SS) surface at room temperature is discussed. It relies on the measurement of the outgassing rate, Q, from the metal surface which is supposed to obey a power law of the form Q = Q10 t-. From the outgassing model the amount of desorbed and adsorbed water vapour was estimated in terms of water monolayers. The investigation was performed at different exposure conditions, i.e., at water vapour pressures from about 1 Pa to 133 Pa and exposure times from about 60 s to 6000 s, on baked AISI 316L EP-SS tubing of the same type to be used in a moisture generator. As expected, the amount of adsorbed water vapour is proportional to both the initial vapour pressure and the exposure time. The paper discusses the outgassing model, gives details of the experimental procedures and apparatus and reports about the experimental results.